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The emerging field of Regenerative Medicine has many definitions; however the NIH's definition, "A treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cell populations or tissues." provides a basis for further discussion of stem cell therapies and their role in daily practice . Regenerative medicine was originally focused on tissue engineering and in vitro growth of replacement organs for transplant. However it has expanded to include other uses including the management of pain and chronic disease.

Table 1

Using the term "stem cells" can elicit emotional responses from people depending on their understanding of the technology and their political and religious orientation. The most controversial stem cell type used for research has been embryonic stem cells. Originally it was believed that embryo's would be the only source of stem cells but further research demonstrated there are numerous sources of viable stem cells including bone marrow, blood vessels, muscle, and adipose tissue. The source of stem cells can alter the potential of the cells to differentiate and ultimately their use. For example, early embryonic cells are usually thought to be totipotent, meaning they can differentiate into almost any type of cell. Adult somatic cells tend to be multipotent meaning they can differentiate into more than one cell type, but only specific cell types in the series of cells derived from the original line (Table 1.) These adult cell types are often referred to by their source (e.g., hematopoietic stem cells, neural stem cells, epidermal stem cells, mesenchymal stem cells, etc.). Interestingly, hematopoietic stem cell therapy has been widely used in human medicine since the 1960's in the form of bone marrow transplant. It is bone marrow and adipose derived mesenchymal stem cells (MSC) which are of current interest to the clinician for the management of pain and orthopedic injury in veterinary medicine.

The use of MSCs for the management of veterinary orthopedic disease was first commercially successful for tendon injuries in horses . They have since been increasingly used for the treatment of osteoarthritis in canine and equine patients. Bone marrow derived mesenchymal stem cells are also being investigated for use in many diseases in veterinary species. The autologus stem cells used for treatment of these conditions are of mesenchymal origin (usually adipose tissue) and seem to be effective by modifying injury healing and altering the local cytokine environment rather than by simply replacing diseased tissue and reversing the anatomy of degenerative tissue with pristine tissue .

Regulatory Considerations for Stem Cell Therapy

Veterinary pharmaceutical therapies are regulated by the FDA-Center for Veterinary Medicine. Cellular and tissue-based treatments are under the authority of the USDA-Center for Veterinary Biologics. Currently neither agency has chosen to regulate veterinary stem cell treatment . This is because current therapies do not exceed regulatory threshold due to minimal processing of autologus cells. However, if future therapies require involved engineering, culturing and cellular processing, the USDA, the FDA, or both may exert their authority and regulate the use of stem cells for therapeutic purposes.

Stem cells are not regulated by the US government and therefore have not received regulatory evaluation for safety or effectiveness. This probably means the use of stem cells should be viewed as an alternative or complementary therapy and thus veterinarians are unlikely to be prosecuted under the Food, Drug, and Cosmetic Act. However, veterinarians should be very careful to obtain informed consent from owners and carefully explain the known benefits, risks, costs, and alternatives to the proposed therapy . Future events and discoveries may alter the way the US government and state veterinary boards choose to classify stem cell therapies so veterinarians need to remain current on their understanding of regulatory requirements.